Arc lamp



Dec. 13, 1949 s, HAWKINS 2,491,178

ARC LAMP Filed June 5, 1947 2 She ets-Sheet l HG] FIG.3 R

FIG. 4

IN VEN TOR. qNK J'vaw HG'WK/NJ AT GENE) Patented Dec. 13., 1949 ARC LAMP Frank Swain Hawkins, Wembley, England, assignor to The General Electric Company, Limited, London, England Application J true 5, 1947, Serial No. 752,606 In Great Britain August 17, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires August 17, 1965 Claims. (Cl. 176-41) The present invention relates to are lamps and is concerned with lamps of the high intensity type employing a positive electrode having a highly mineralised core (that is a core with a mineral content greater than 25%) of relatively large diameter, that is a diameter not less than one third of that of the electrode, and in which the current density is not less than 50 amperes per square centimeter of unburnt cross-sectional area of the positive electrode. The unburnt cross-sectional area is the cross-sectional area at a point back from the tapering portion at the end of the electrode. The operating current density is usually of the order of 70-100 amperes per square centimeter of unburnt cross-sectional area and a deep crater is formed in the end of the positive electrode. Such lamps are used for example in cinema studios for the taking of colour films.

They suiier from the disadvantage that they are not quite silent in operation and the slight noise produced is undesirable when sound films are being made.

The voltage drop across the arc terminals is usually about 65 volts whereas the lamps are often required to operate from a 115 volt D. C. circuit. It is therefore necessary to drop 50 volts in a ballast resistance connected in series with the arc. A certain voltage drop in a ballast resistance is necessary in order to stabilise the are but the drop referred to is considerably in excess of what is needed for this purpose. The large power loss in the stabilising resitance is disadvantageous for reasons of economy and because of the heat given off thereby which is often undesirable, for instance in a cinema studio.

It is the principal object of the present invention to provide an arc lamp or a combination of arc lamps in which the disadvantages above referred to are substantially reduced.

According to the present invention an arc lamp of the type specified has a plurality of negative electrodes, each associated with a separate series ballast resistance, the said negative electrodes co-operating, in parallel, with a single positive electrode. The number of negative electrodes employed is usually small, for example two or three. The negative electrodes are preferably disposed in such a manner as to spread the negative flame relatively uniformly over the positive crater.

It has been found that with an arc lamp according to this invention the noise above referred to is substantially reduced.

It has also been found that the voltage drop across the arc is reduced and may for example be about 45-50 volts. If the voltage of the D. C. supply has the usual value of volts, and if a. single lamp were operated across this supply, a ballast resistance even larger than before would be needed. However, the lower voltage drop has the advantage of permitting two lamps according to the present invention to be operated in series. It has been found that two such lamps in series constitute a stable system burning steadily and quietly. The voltage drop needed in the ballast resistance may then be for example only about 5-25 volts which is nevertheless suflicient for stability.

According to a further feature of the present invention therefore a plurality of arc lamps according to the invention are connected to operate in series with a direct current supply whose voltage is such that the voltage drop across each of said are lamps and the ballast resistances associated therewith is more than 47 volts but less than 63 volts.

In the drawings in which there are illustrated various embodiments of my invention,

Fig. 1 is a diagrammatic showing of a circuit arrangement of electrodes in accordance with my invention, the electrodes being illustrated in end elevation;

Fig. 2 is a view similar to Fig. 1 but with the electrodes shown in plan;

Figs. 3 and 4 are views similar to Figs. 1 and 2, respectively, of an arrangement of electrodes embodying a modified form of my invention;

Fig. 5 is a view similar to Fig. 2 of an arrangement of electrodes embodying another modified form of my invention;

Figs. 6 and 7 are views similar to Figs. 1 and 2, respectively, of an arrangement of electrodes embodying still another modified form of my invention; and

Fig. 8 is a view similar to Fig. 1 of an arrangement ofelectrodes embodying yet another modifled form of my invention.

In the arrangement of Figs. 1 and 2, two negative electrodes I, 2 are used which are arranged with their tips 3, 4 facing the tip 5 of the positive electrode 6, at an angle of about 30 to the horizontal, assuming the positive electrode to be horizontal, and are disposed symmetrically on either side of a vertical plane through the positive electrode 6, each being at an angle of about 50 to the vertical plane. The positive electrode 6 may be of 16 mm. diameter and the negative electrodes of 8 mm. diameter. Two ballast resistors R, which may be variable, have their one terminal N connected to a negative electrode and their other terminal connected, in common, to the negative supply terminal. The positive electrode is connected directly to the positive supply terminal P. As already explained, two lamps with their associated resistors as described may be connected in series as shown in Fig. 8. If the supply voltage is suitable, more than two lamps may be connected in series.

In the arrangement of Figs. 3 and 4, the three negative electrodes I, 8 and 9 are arranged facing the positive electrode 10 which is horizontal; the negative electrodes 1 and 9 being above the positive electrode l and making an angle of about 30 degrees with the horizontal, and the negative electrode 8 being below the positive electrode l0 and making an angle of about 70 degrees with the horizontal. The axis of the negative electrode 8 lies in the same vertical plane as the axis of the positive electrode Ill and the negative electrodes 1 and 9 are disposed symmetrically on either side of this vertical plane at an angle of about 50 degrees.

In the arrangement of Fig. 5, axes of the two negative electrodes II and I2 are parallel, and are perpendicular to the axis of the positive electrode [3. If the positive electrode I3 is of 16 mm. diameter and the negative electrodes H and I2 are of 8 mm. diameter, the negative electrodes H and i2 are placed with their axes about 16 mm. apart and the electrode tips opposite the periphcry of the positive electrode IS.

The preferred arrangement is illustrated in Figures 6 and 7 and is similar to the arrangement illustrated in Figures 3 and 4 with the exception that only two negative electrodes 1 and 9 are used in conjunction with the positive electrode In.

It is to be understood that although the positive electrode has been assumed horizontal in the above arrangement, it may in fact be arranged at any required angle with the negative electrodes correspondingly disposed.

Preferably known means of magnetically controlling the arc are used in the above arrangements.

I claim:

1. In combination, in a high intensity carbon arc lamp, a cored positive carbon electrode, said core having a mineral content in excess of 25%, and being adapted to operate at a current density in excess of 50 amperes per square centimeter, and at least two negative carbon electrodes, all

said negative electrodes co-operating in parallel with said positive electrode.

2. In combination, in a high intensity carbon arc lamp a cored positive carbon electrode, said core having a mineral content in excess of 25% and being adapted to operate at a current density in excess of 50 amperes per square centimeter, means for carrying said positive electrode, at least two negative carbon electrodes, means for carrying each of said negative electrodes, said means for carrying said positive electrode and said means for carrying said negative electrodes being so disposed that all the negative electrodes cooperate with the said single positive electrode to spread the negative flame relatively uniformly over the crater formed in the end of said positive electrode.

3. In combination, in a high intensity carbon arc lamp, a cored positive carbon electrode, said core having a mineral content in excess of 25% and adapted to operate at a current density in excess of 50 amperes per square centimeter, means for carrying said positive carbon electrode, at least two negative carbon electrodes, means for carrying each of said negative carbon electrodes, said negative carbon electrode carrying means being so disposed with respect to the means for carrying the said positive carbon electrode that the tips of said negative electrodes lie in a plane substantially normal to the axis of said positive electrode whilst the angles between the axis of the carbon positive electrode and the axis of each negative electrodes are substantially the same and are each not less than ninety degrees.

4. In combination, in a high intensity electric carbon arclamp, a cored positive carbon electrode, a plurality of negative carbon electrodes, a plurality of ballast resistance elements, each of said ballast resistance elements being associated with a separate negative electrode and all said negative electrodes co-operating in pararrel with said positive electrode and a source of direct current electrical energy, the voltage of said source and the value of said ballast resistances being such that the current density in said cored positive carbon electrode is at least 50 amperes per square centimeter of unburnt crosssectional area.

5. In combination, two high intensity electric carbon arc lamps as claimed in claim 4 and a source of direct current electrical energy, said are lamps being connected in series across said source and the voltage of said source being such that the voltage drop across each of said lamps and the ballast resistance associated therewith is at least 47 volts but not greater than 63 volts.

FRANK SWALN HAWKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Thomson July 7, 1885 Vineing Aug. 9, 1892 Hunter Mar. 14, 1893 Gerdien Apr. 20, 1926 Parisot Jan. 2, 1940 

